New Developments at the ALS High-Pressure Beamline 12.2.2

Abstract:

ALS-beamline 12.2.2 celebrated its 10-year anniversary as a beamline collaboratively operated by the ALS and COMPRES. The anniversary coincided with a major rebuild and expansion of its capabilities for in-situ high-pressure and high-temperature X-ray diffraction.

A rebuild of the 12.2.2 laser heating table was completed and commissioned in the past year. The new design relies on a vertically positioned small (~1m x 1m) breadboard that is placed perpendicularly to the incident X-ray beam next to the sample stage. Upstream and downstream viewing-, IR-laser and pyrometry-optics are mounted on opposite surfaces of the breadboard. On-line ruby fluorescence optics including a blue diode laser are also mounted on the upstream surface. The much reduced dimensions of the design lead to smaller mechanical lever arms and thus to a significant suppression of vibrations. This was confirmed in the commissioning phase with high-quality optical images (~ 2 μm resolution) as well as a very stable hotspot in DAC samples. A further optimized pyrometry code was cross-calibrated against thermal expansions of Pt and Ta, and was found to agree with those values within experimental uncertainties. Pyrometry relies on imaging the full hot-spot onto a spectrometer and combining the thus obtained average temperature with an intensity map collected at 700 nm to produce a temperature contour map of the entire sample chamber. Besides axial laser heating, double-sided radial laser heating is also being developed and commissioned.

The X-ray source of 12.2.2 makes it an ideal station to focus on high-pressure single crystal diffraction. The present set-up operates parasitically with a single rotation axis on the in-situ laser heating powder diffraction sample stage in concert with a fast (15 fps) amorphous silicon/diode array detector. Although this set-up poses limitations with respect to accessible reciprocal space, high pressure single crystal structure solution and refinements of organic compounds incl. anisotropic displacement parameters have been demonstrated. Imminent development plans aim for the installation of a rugged multi-axis diffractometer on its own dedicated end-station in combination with with a compact fast detector on the 2-theta arm. This will be capable of carrying state of the art wide opening angle DAC's (BX90).